Vacua

noun

1. A region of space that contains no matter.
2. (plural only "vacuums") A vacuum cleaner.
3. The condition of rarefaction, or reduction of pressure below that of the atmosphere, in a vessel, such as the condenser of a steam engine, which is nearly exhausted of air or steam, etc.

   "a vacuum of 26 inches of mercury, or 13 pounds per square inch"

4. A spacetime having tensors of zero magnitude